This invention relates to a device and a method for reducing asymmetry in the wings of an aircraft. More particularly, this invention relates to reducing asymmetry in the wings of an aircraft by preventing an aircraft""s flap/slat actuation system from acting in an unplanned and abnormal fashion.
In designing aircraft wings, a designer must ensure that the wings produce an appropriate lifting force during cruising, landing, and takeoff conditions. Each of these conditions require the aircraft""s wings to be configured in a different manner so that an appropriate lifting force is produced. The lifting force produced by an aircraft""s wings may be calculated by the formula (xc2xdxcfx81V2)xc3x97(coefficient of lift)xc3x97(wing area), where xcfx81 is the density of the air and V is the velocity of the aircraft.
During cruising conditions, the aircraft""s velocity (typically between 400-600 mile per hour) is generally constant. The aircraft""s altitude (typically between 25,000 and 35,000 feet) is also generally constant. The density of the air during cruising conditions is also generally constant because air density is directly related to the altitude at which the air is measured.xe2x80x94i.e., as the altitude increases the density of the air decreases and as the altitude decreases the density of the air increasesxe2x80x94. Using the formula described above, the aircraft""s velocity is the component that has the greatest impact on the lifting force produced during cruising conditions.
However, when an aircraft begins an approach for landing or begins to taxi for takeoff, its velocity is considerably lower than at cruising conditions. At these lower velocities, the wings may still produce enough lift to carry the aircraft""s weight because the air at lower altitudes is denser than the air at cruising altitudes.
Although the wings may produce enough lift, during landing and take off conditions the lift produced is usually not sufficient to accomplish either within a reasonable runway length. To compensate for the lower velocities during landing and takeoff, auxiliary devices (high-lift devices) are added to the leading and trailing edges of the wings to increase the wing""s effective camber and area. From the formula described above, increasing the wing""s effective camber and area coupled with the increased air density compensates for the lower velocities and allows for a lift to be produced substantially similar to those developed during cruising conditions. The high-lift devices on the leading edge of the aircraft""s wing are usually called slats and those added to the trailing edges of the wing are usually called flaps.
FIG. 1 shows one embodiment of aircraft 2 which includes Power Drive Unit (PDU) 5, slat 10, wing tip brake 15, flap 20, drive shaft line 25, local actuator 30, and wing 35. In practice, it is customary to have a plurality of slats, wing tip brakes, flaps, drive shaft lines, local actuators, and wings on the aircraft.
Each slat 10 and flap 20 may be installed on the aircraft""s airframe at an appropriate point on the wing. Slat 10 and flap 20 are driven by local actuator 30 and by drive shaft line 25. Drive shaft line 25 may be routed down the leading and trailing edges of wing 35. PDU 5 may provide power to local actuator 30 and drive shaft line 25.
It is also customary to equip each local actuator 30 with a torque limiter (not shown in FIG. 1) because drive shaft line 25 is capable of delivering many times the torque that local actuator 30 could withstand. To prevent local actuator 30 from experiencing excessive torque, each torque limiter may sense the torque that is being transmitted to its associated local actuator. If the torque limiter senses excessive torque, then it may cause wing tip brake 15 to be applied and lock down drive shaft line 25. Each actuator and torque limiter is preferably connected to one of a plurality of drive shaft lines.
When utilizing slats and flaps, it is important to avoid the development of asymmetries in the aircraft""s wingsxe2x80x94e.g., where slats and flaps on one side of the plane are deployed at a different position than slats and flaps on the other side of the plane, leading to an uneven distribution of lift on the wings that may contribute to instability of the planexe2x80x94. Asymmetries may develop from many possible causes. For example, if one of the drive shaft lines breaks, then all the slat or flap panels outboard of the break will not be driven by or controlled by the PDU. In addition, if the slat or flap panels outboard of the break are extended, they may be blown back to a cruising position by aerodynamic loads placed upon them. This condition is known as xe2x80x9cblow back.xe2x80x9d Although, the normal flying controls on an aircraft are designed to correct some asymmetry in the slats and flaps, they are not designed to offset the asymmetry that occurs when an aircraft experiences blow back conditions.
To rectify this exigency, aircraft with high lift systems typically have asymmetry detection devices (not shown in FIG. 1), which compare the position of the slats and flaps on each wing. If there are differences exceeding a preset allowance, the asymmetry detection device may immediately apply wingtip brake 15 that may lock slat 10 and flap 20 on each wing 35.
One disadvantage of the wingtip brake is that it is large and heavy. A further disadvantage of the wingtip brake is that the drive shaft line that connects the individual slats and flaps to the wingtip brake might actually be interrupted at several points. For example, due to an engine burst, the drive shaft line might be severed at several points, thus leaving some parts of the drive shaft line not coupled to any brake. The present invention addresses these shortcomings.
It therefore would be desirable to provide a drive shaft line braking device that is small and lightweight.
It would also be desirable to provide a drive shaft line braking device that brakes the drive shaft line at each local actuator.
Therefore, it is an object of this invention to provide a drive shaft line braking device that is small and lightweight.
It is also an object of this invention to provide a drive shaft line braking device that brakes the drive shaft line at each local actuator.
In accordance with this invention, an apparatus including a two-brake torque limiting device used to fix the position of one or more flaps or slats on an airplane wing is provided. The two-brake torque limiting device preferably includes a speed-increasing gear, a trigger brake, and a lock down brake.
The speed-increasing gear is preferably coupled to a drive shaft line. The speed-increasing gear rotates at a rotational speed proportionally related to and faster than a rotational speed of the drive line shaft.
The trigger brake is preferably coupled to the speed-increasing gear. The trigger brake may apply a braking force to the speed-increasing gear when a control signal is received.
The lock down brake is preferably coupled to the speed-increasing gear. The lock down may apply a braking force to the drive line shaft. The braking force may be based upon the rotational motion of the speed-increasing gear, the drive shaft line, and/or a combination of the rotational motion of the speed-increasing gear and the rotational motion of the drive shaft line.